Transient current planning method for ultra-high-speed permanent magnet synchronous motor for improving speed regulation response capabilities

ABSTRACT

A transient current planning method for an ultra-high-speed permanent magnet synchronous motor for improving speed regulation response capabilities is provided. A transient current planning module uses a voltage model considering transient current changes to calculate current instruction values of an ultra-high-speed permanent magnet synchronous motor under MTPA control, general flux-weakening control, and MTPV control; a mode switching condition judgment subsystem judges whether a control mode is MTPA control or general flux-weakening control, or MTPV control, and sends d- and q-axis current instruction values in the corresponding control mode to a voltage decoupling control module; and the voltage decoupling control module calculates d- and q-axis voltage instruction values for controlling the motor, so as to realize control over the ultra-high-speed permanent magnet synchronous motor.

CROSS REFERENCE TO THE RELATED APPLICATIONS

This application is the national phase entry of InternationalApplication No. PCT/CN2021/071268, filed on Jan. 12, 2021, which isbased upon and claims priority to Chinese Patent Application No.202010850957.0, filed on Aug. 21, 2020, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to the field of control overultra-high-speed permanent magnet synchronous motors, and in particular,to a transient current planning method for an ultra-high-speed permanentmagnet synchronous motor for improving speed regulation responsecapabilities.

BACKGROUND

An ultra-high-speed permanent magnet synchronous motor is applied toscenarios such as ultra-high-speed motorized spindles and high-powerfuel cell dedicated air compressors, and is an important core component.Ultra-high-speed permanent magnet synchronous motors can currently meetrequirements for the limit rotational speed in ultra-high-speedapplication scenarios, but speed regulation response capabilities of theultra-high-speed permanent magnet synchronous motors are stillunsatisfactory. Actually, since current trajectories are all derivedbased on steady-state voltage models in current planning ofultra-high-speed permanent magnet synchronous motors, a current workingpoint derived in the process of motor speed regulation is not a maximumelectromagnetic torque output at the rotational speed, thus restrictingthe speed regulation response of the motors.

Speed regulation response capabilities of ultra-high-speed permanentmagnet synchronous motors are improved mostly in active disturbancerejection control in the prior art. Chinese Patent (CN107425769A) hasdisclosed an active disturbance rejection control method and system fora permanent magnet synchronous motor speed regulation system. A fuzzyadaptive sliding mode speed control method is used to weaken theover-regulation phenomenon in the speed control process and increase thesystem response speed; feedback compensation of an extended stateobserver is used to improve the disturbance rejection capabilities ofthe system, and an internal model current control strategy is used toincrease the d- and q-axis current response speed. The patent has theproblem of essentially using a disturbance compensation method toimprove the disturbance rejection capabilities so as to improve speedregulation response, which cannot increase the maximum torque that canbe output by a motor in the process of speed regulation, thus providinglimited improvement in speed regulation response capabilities.

Chinese patent (CN110289795A) has disclosed a control system and acontrol method for a permanent magnet synchronous motor for an electricvehicle. A pre-established disturbance-adaptive active disturbancerejection model is used to process rotor and current signals to obtain acontrol output signal, and an extended state observer is used to observea load torque to improve the adjustment precision of a control gain, soas to improve the anti-interference capability of the permanent magnetsynchronous motor speed regulation system, thereby enhancing speedregulation response. The patent improves the anti-interferencecapability by increasing the adjustment precision of the control gain,but still has not improved the output capability of a maximumelectromagnetic torque of the motor at a certain rotational speed, andthus there's still a lot of room for improvement in speed regulationresponse capabilities.

SUMMARY

In view of the deficiencies in the prior art, the present inventionprovides a transient current planning method for an ultra-high-speedpermanent magnet synchronous motor for improving speed regulationresponse capabilities, which enables the motor to output a maximumelectromagnetic torque during operation at any rotational speed andimproves speed regulation response capabilities of the motor.

The present invention achieves the aforementioned technical objective bythe following technical means.

A transient current planning method for an ultra-high-speed permanentmagnet synchronous motor for improving speed regulation responsecapabilities, wherein a transient current planning system on which thetransient current planning method is based includes a transient currentplanning module, and the transient current planning module includes aMTPA control subsystem, a general flux-weakening control subsystem, aMTPV control subsystem, and a mode switching condition judgmentsubsystem; the MTPA control subsystem calculates d- and q-axis currentinstruction values under MTPA control, the general flux-weakeningcontrol subsystem calculates d- and q-axis current instruction values ina general flux-weakening control stage, the MTPV control subsystemcalculates d- and q-axis current instruction values in a MTPV controlstage, the mode switching condition judgment subsystem judges whether acontrol mode is a MTPA control or general flux-weakening control or MTPVcontrol, and sends the d- and q-axis current instruction values in thecorresponding control mode to a voltage decoupling control module, andthe voltage decoupling control module calculates d- and q-axis voltageinstruction values for controlling the motor;

the transient current planning method includes the following steps:

step (1): judging, by the mode switching condition judgment subsystem,whether to switch to general flux-weakening control or MTPV control, andif yes, entering step (2); otherwise, entering step (5), wherein

the switching or not is determined by judging whether d- and q-axisvoltage values reach limit values as a switching point, and a judgmentformula is:√{square root over (U _(d) ² +U _(q) ²)}<U _(max)

if the judgment formula is established, switching to MTPA control isperformed; otherwise, the method turns to step (2);

step (2): judging, by the mode switching condition judgment subsystem,whether an electrical angular velocity sampling value ω_(r) is greaterthan a MTPV control starting point rotational speed ω_(r), and if not,entering step (3); if yes, entering step (4);

step (3): receiving, by the general flux-weakening control subsystem, d-and q-axis current instruction values I_(d)* and I_(q)* in a MTPAcontrol stage and the electrical angular velocity sampling value, andcalculating d- and q-axis current instruction values in the generalflux-weakening control stage, wherein

the d-axis current instruction value in the general flux-weakeningcontrol stage is:a ₁ ² I _(d)*²+2a ₁ a ₂ I _(d) *+a ₂ ² +b ₁ ²(I _(max) ² −I _(d)*²)+b ₂²+2b ₁ b ₂√{square root over (I _(max) ² −I _(d)*²)}=U _(max) ²

in the formula, a₁, a₂, b₁, b₂, A, and B are all variables, anda₁=ω_(r)L_(d), a₂=ω_(r)λ_(PM)+L_(q)B, B=dI_(q)/dt, b₁=ω_(r)L_(q),b₂=L_(d)A, A=dI_(d)/dt; I_(max) is a maximum stator current, λ_(PM) is apermanent magnet flux linkage, L_(d) is a d-axis inductance, L_(q) is aq-axis inductance, I_(q) is aq-axis current instruction initial value,and I_(d) is a d-axis current instruction initial value;

the q-axis current instruction value in the general flux-weakeningcontrol stage is:I _(q)*=√{square root over (I _(max) ² −I _(d)*²)}

step (4): receiving, by the MTPV control subsystem, the electricalangular velocity sampling value ω_(r) and d- and q-axis current samplingvalues i_(d) and i_(q), and calculating d- and q-axis currentinstruction values in the MTPV control stage, wherein

a calculation formula of the d-axis current instruction value in theMTPV control stage is:

${\frac{{\left( {\rho - 1} \right)L_{d}A} - \sqrt{{\left( {\rho - 1} \right)^{2}L_{d}^{2}A^{2}} + {4\left( {\rho - 1} \right)\omega_{r}L_{q}C}}}{2\omega_{r}L_{q}} - \frac{C}{\sqrt{U_{\max}^{2} - \left( {{\omega_{r}L_{d}I_{d}^{*}} + {\lambda_{PM}\omega_{r}} + {L_{q}B}} \right)^{2}}}} = 0$

a calculation formula of the q-axis current instruction value in theMTPV control stage is:

$I_{q}^{*} = \frac{C}{\left( {\rho - 1} \right)\sqrt{U_{\max}^{2} - \left( {{\omega_{r}L_{d}I_{d}^{*}} + {\lambda_{PM}\omega_{r}} + {L_{q}B}} \right)^{2}}}$

in the formulas, p and C are both variables, and ρ=L_(d)/L_(q),C=ρω_(r)[λ_(PM)/L_(q)+(ρ−1)I_(d)*][L_(d)I_(d)*+λ_(PM)+BL_(q)/ω_(r)]; and

step (5): receiving, by the voltage decoupling control module, the d-and q-axis current instruction values sent by the transient currentplanning module and calculating d- and q-axis voltage instructions, soas to realize control over the ultra-high-speed permanent magnetsynchronous motor.

As a further technical solution, a process of obtaining the d- andq-axis current instruction values in the MTPA control stage is: judgingwhether I_(q) is greater than a maximum q-axis current wherein if yes, acalculation formula of the d- and q-axis current instruction values is:

$\left\{ {\begin{matrix}{I_{d}^{*} = {\frac{\lambda_{PM}}{4\left( {L_{q} - L_{d}} \right)} - \sqrt{\frac{\lambda_{PM}^{2}}{16\left( {L_{q} - L_{d}} \right)^{2}} + \frac{I_{\max}^{2}}{2}}}} \\{I_{q}^{*} = {{{sign}\left( n^{*} \right)}\sqrt{I_{\max}^{2} - I_{d\max 1}^{2}}}}\end{matrix};} \right.$if not, a calculation formula of the d- and q-axis current instructionvalues is:

$\left\{ {\begin{matrix}{I_{d}^{*} = {\frac{\lambda_{PM}}{4\left( {L_{q} - L_{d}} \right)} - \sqrt{\frac{\lambda_{PM}^{2}}{16\left( {L_{q} - L_{d}} \right)^{2}} + I_{q}^{2}}}} \\{I_{q}^{*} = I_{q}}\end{matrix},} \right.$wherein sign(n*) is a sign function.

As a further technical solution, a calculation formula of the maximumcurrent I_(qmax1) is:

$\left\{ {\begin{matrix}{I_{d\max 1} = {\frac{\lambda_{PM}}{4\left( {L_{q} - L_{d}} \right)} - \sqrt{\frac{\lambda_{PM}^{2}}{16\left( {L_{q} - L_{d}} \right)^{2}} + \frac{I_{\max}^{2}}{2}}}} \\{I_{q\max 1} = \sqrt{I_{\max}^{2} - I_{d\max 1}^{2}}}\end{matrix},} \right.$wherein I_(d max1) is a maximum d-axis current under MTPA control.

As a further technical solution, the q-axis current instruction initialvalue is obtained from

${T_{e} = {\frac{1}{2}{n_{p}\left\lbrack {\lambda_{PM} + \sqrt{\lambda_{PM}^{2} + {4{I_{q}^{2}\left( {L_{d} - L_{q}} \right)}^{2}}}} \right\rbrack}I_{q}}}{and}{{T_{e} = {\frac{\omega_{ref} - \omega_{r}}{\Delta t}J}},}$wherein T_(e) is an electromagnetic torque, ω_(ref) is a targetrotational speed, Δt is a sampling interval, J is a shaft moment ofinertia, and n_(p) is a number of pole-pairs.

As a further technical solution, the MTPV control starting pointrotational speed is calculated by combining the d and q currentinstruction values in the MTPV control stage and a current limit circleequation, which is specifically:

$\left\{ {\begin{matrix}\begin{matrix}{\frac{{\left( {\rho - 1} \right)L_{d}A} - \sqrt{{\left( {\rho - 1} \right)^{2}L_{d}^{2}A^{2}} + {4\left( {\rho - 1} \right)\omega_{Vs}L_{q}C}}}{2\omega_{Vs}L_{q}} -} \\{\frac{C}{\sqrt{U_{\max}^{2} - \left( {{\omega_{Vs}L_{d}I_{d}^{*}} + {\lambda_{PM}\omega_{Vs}} + {L_{q}B}} \right)^{2}}} = 0}\end{matrix} \\{I_{q}^{*} = \frac{C}{\left( {\rho - 1} \right)\sqrt{U_{\max}^{2} - \left( {{\omega_{Vs}L_{d}I_{d}^{*}} + {\lambda_{PM}\omega_{Vs}} + {L_{q}B}} \right)^{2}}}} \\{{I_{d}^{*2} + I_{q}^{*2}} = I_{\max}^{2}}\end{matrix}.} \right.$

As a further technical solution, values of A and B in the generalflux-weakening control stage A, B are:

$\left\{ \begin{matrix}{A = \frac{I_{d1} - I_{dr}}{\Delta t}} \\{B = \frac{I_{q1} - I_{qr}}{\Delta t}}\end{matrix} \right.$

wherein I_(dr) and I_(qr) are respectively d- and q-axis currentsampling values; I_(d1) and I_(q1) are respectively the d- and q-axiscurrent instruction values in the general flux-weakening control stage,which are specifically:

$\left\{ {\begin{matrix}{I_{d1} = \frac{{L_{d}\lambda_{PM}} - {L_{q}\sqrt{\lambda_{PM}^{2} + {\left( {L_{q}^{2} - L_{d}^{2}} \right)\left( {I_{\max}^{2} - \frac{U_{\max}^{2}}{\omega_{r}^{2}L_{q}^{2}}} \right)}}}}{L_{q}^{2} - L_{d}^{2}}} \\{I_{q1} = \sqrt{I_{\max}^{2} - I_{d1}^{2}}}\end{matrix}.} \right.$

As a further technical solution, values of A and B in the MTPV controlstage are:

$\left\{ \begin{matrix}{A = \frac{I_{d2} - I_{dr}}{\Delta t}} \\{B = \frac{I_{q2} - I_{qr}}{\Delta t}}\end{matrix} \right.$

wherein I_(d2) and I_(q2) are respectively the d- and q-axis currentinstruction values in the MTPV control stage, which are specifically:

$\left\{ \begin{matrix}{I_{d2} = {{- \frac{\lambda_{PM}}{L_{d}}} + E}} \\{I_{q2} = \frac{\sqrt{\left( {U_{\max}/\omega_{r}} \right)^{2} - \left( {L_{d}E} \right)^{2}}}{L_{q}}} \\{E = \frac{{\rho\lambda_{PM}} - \sqrt{\left( {\rho\lambda_{PM}} \right)^{2} + {8\left( {\rho - 1} \right)^{2}\left( {U_{\max}/\omega_{r}} \right)^{2}}}}{4\left( {\rho - 1} \right)L_{d}}}\end{matrix} \right.$

wherein in the formula, E is a variable.

The beneficial effects of the present invention are: in the presentinvention, a transient current planning module is established and uses avoltage model considering transient current changes to calculate currentinstruction values of an ultra-high-speed permanent magnet synchronousmotor in a general flux-weakening control stage and a MTPV control stageto obtain a current trajectory; meanwhile, a mode switching conditionjudgment subsystem judges whether the ultra-high-speed permanent magnetsynchronous motor should use MTPA control or general flux-weakeningcontrol or MTPV control, and outputs d- and q-axis current instructionsin the control stage to a voltage decoupling control module; and thevoltage decoupling control module calculates d- and q-axis voltageinstruction values so as to realize control over the ultra-high-speedpermanent magnet synchronous motor. The present invention caneffectively improve dynamic characteristics of the ultra-high-speedpermanent magnet synchronous motor in the speed regulation process,achieve more precise torque output capability of the motor, and enablethe motor to output the maximum electromagnetic torque that can beexerted by the motor during operation at any rotational speed, andenhance speed regulation response capabilities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an architecture diagram illustrating control over anultra-high-speed permanent magnet synchronous motor in the presentinvention;

FIG. 2 is a flowchart illustrating transient current trajectory planningfor the ultra-high-speed permanent magnet synchronous motor in thepresent invention; and

FIG. 3 is a diagram illustrating a changing trend of a currenttrajectory before and after transient current changes are considered.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention is further illustrated below with reference to theaccompanying drawings and specific embodiments, but the protection scopeof the present invention is not limited thereto.

FIG. 1 shows a transient current planning system for an ultra-high-speedpermanent magnet synchronous motor for improving speed regulationresponse capabilities. A transient current planning module isestablished. The module receives a target rotational speed ω_(ref), anelectrical angular velocity sampling value U) and d- and q-axis currentsampling values i_(d), i_(q), and uses a voltage model consideringtransient current changes to calculate current instruction values of theultra-high-speed permanent magnet synchronous motor under MTPA control,general flux-weakening control, and MTPV control to obtain a currenttrajectory; meanwhile, the transient current planning module uses givenswitching rules to judge a control mode (MTPA control or generalflux-weakening control or MTPV control) that should be adopted by theultra-high-speed permanent magnet synchronous motor, and outputs andq-axis current instructions I_(d)*, I_(q)* in the control mode to avoltage decoupling control module; and the voltage decoupling controlmodule calculates and q-axis voltage instruction values U_(d)* andU_(q)*, so as to realize control over the ultra-high-speed permanentmagnet synchronous motor.

The transient current planning module includes a MTPA control subsystem,a general flux-weakening control subsystem, a MTPV control subsystem,and a mode switching condition judgment subsystem.

As shown in FIG. 2 , a transient current planning method for anultra-high-speed permanent magnet synchronous motor for improving speedregulation response capabilities specifically includes the followingsteps:

Step (1): a rotational speed command is input.

Step (2): a transient current planning module receives a targetrotational speed ω_(ref), an electrical angular velocity sampling valueω_(r) and d- and q-axis current sampling values i_(d) and i_(q).

Step (3): a q-axis current instruction initial value I_(q) is obtainedby a rotational speed regulator and a PI regulator, and I_(q) is inputto a MTPA control subsystem.

The q-axis current instruction initial value I_(q) is obtained throughthe following method:

-   -   1) a required electromagnetic torque is calculated by the        rotational speed regulator and the PI regulator, where a        calculation formula is:

$\begin{matrix}{T_{e} = {\frac{\omega_{ref} - \omega_{r}}{\Delta t}J}} & (1)\end{matrix}$

where in the formula, Δt is a sampling interval, and J is a shaft momentof inertia.

2) A relation between the torque and the q-axis current initial valueI_(q) is calculated according to an electromagnetic torque equation anda current limit equation:T _(e)=½n _(p)[λ_(PM)+√{square root over (λ_(PM) ²+4I _(q) ²(L _(d) −L_(q))²)}]I _(q)  (2)

where in the formula, n_(p) is a number of pole-pairs, λ_(PM) is apermanent magnet flux linkage, L_(d) is a d-axis inductance, and L_(q)is a q-axis inductance.

The current instruction initial value I_(q) is obtained from formulas(1) and (2).

Step (4): the MTPA control subsystem calculates and q-axis currentinstruction values in a MTPA control stage.

-   -   1) A maximum q-axis current i_(qmax1) under MTPA control is        calculated, where a calculation formula is:

$\begin{matrix}\left\{ \begin{matrix}{I_{d\max 1} = {\frac{\lambda_{PM}}{4\left( {L_{q} - L_{d}} \right)} - \sqrt{\frac{\lambda_{PM}^{2}}{16\left( {L_{q} - L_{d}} \right)^{2}} + \frac{I_{\max}^{2}}{2}}}} \\{I_{q\max 1} = \sqrt{I_{\max}^{2} - I_{d\max 1}^{2}}}\end{matrix} \right. & (3)\end{matrix}$

wherein the formula, I_(d max1) is a maximum d-axis current under MTPAcontrol, and I_(max) is a maximum stator current.

2) It is judged whether I_(q) is greater than I_(qmax1), and if yes, acalculation formula of the d- and q-axis current instruction values is:

$\begin{matrix}\left\{ \begin{matrix}{I_{d}^{*} = {\frac{\lambda_{PM}}{4\left( {L_{q} - L_{d}} \right)} - \sqrt{\frac{\lambda_{PM}^{2}}{16\left( {L_{q} - L_{d}} \right)^{2}} + \frac{I_{\max}^{2}}{2}}}} \\{I_{q}^{*} = {{sign}\left( n^{*} \right)\sqrt{I_{\max}^{2} - I_{d\max 1}^{2}}}}\end{matrix} \right. & (4)\end{matrix}$

if not, a calculation formula of the d- and q-axis current instructionvalues is:

$\begin{matrix}\left\{ \begin{matrix}{I_{d}^{*} = {\frac{\lambda_{PM}}{4\left( {L_{q} - L_{d}} \right)} - \sqrt{\frac{\lambda_{PM}^{2}}{16\left( {L_{q} - L_{d}} \right)^{2}} + I_{q}^{2}}}} \\{I_{q}^{*} = I_{q}}\end{matrix} \right. & (5)\end{matrix}$

where in the formula, sign(n*) is a sign function.

Step (5): a mode switching condition judgment subsystem judges whetherto switch to general flux-weakening control or MTPV control, and if yes,the method enters step (6); otherwise, the method enters step (9).

The judging whether to switch to general flux-weakening control or MTPVcontrol is achieved by judging whether d- and q-axis voltage valuesreach limit values as a switching point, and a judgment formula is:√{square root over (U _(d) ² +U _(q) ²)}<U _(max)  (6)

where in the formula, U_(max) is a terminal voltage limit value.

If formula (6) is established, switching to MTPA control is performed;if the condition is not established, the method turns to step (6) tofurther judge the control mode.

Step (6): the mode switching condition judgment subsystem judges whetherthe electrical angular velocity sampling value is greater than a MTPVcontrol starting point rotational speed, namely, ω_(r)≥ω_(v), and ifnot, the method enters (7); if yes, the method enters step (8).

Step (7): a general flux-weakening control subsystem receives the d- andq-axis current instruction values calculated in step (4) and theelectrical angular velocity sampling value, and calculates d- and q-axiscurrent instruction values in the general flux-weakening control stage,and the method enters step (9).

The derivation process of the d- and q-axis current instruction valuesunder general flux-weakening control considers transient current changesto improve precise response of a torque in the general flux-weakeningcontrol stage, enlarge the torque output range of the motor, and achievethe purpose of enhancing speed regulation response capabilities.

A voltage model considering transient current changes is:

$\begin{matrix}\left\{ \begin{matrix}{U_{d} = {{RI}_{d} + {L_{d}\frac{{dI}_{d}}{dt}} - {\omega_{r}L_{q}I_{q}}}} \\{U_{q} = {{RI}_{q} + {L_{q}\frac{{dI}_{q}}{dt}} + {\omega_{r}\left( {{L_{d}I_{d}} + \lambda_{PM}} \right)}}}\end{matrix} \right. & (7)\end{matrix}$

wherein the formula, R is a stator resistance, and I_(d) is a d-axiscurrent instruction initial value.

In current applications, in order to derive a current trajectoryinstruction more conveniently, transient current voltage drop terms

$L_{d}\frac{{dI}_{d}}{dt}{and}L_{q}\frac{{dI}_{q}}{dt}$in formula (7) are usually omitted, while the control system provided inthe present invention considers transient current voltage drop terms.

After transient current changes are considered, a calculation formula ofthe d-axis current instruction value in the general flux-weakeningcontrol stage is:a ₁ ² I _(d)*²+2a ₁ a ₂ I _(d) *+a ₂ ² +b ₁ ²(I _(max) ² −I _(d)*²)+b ₂²+2b ₁ b ₂√{square root over (I _(max) ² −I _(d)*²)}=U _(max) ²  (8)

wherein the formula, a₁, a₂, b₁, b₂, A, and B are all variables, anda₁=ω_(r)L_(d), a₂=ω_(r)λ_(PM)+L_(q)B, B=dI_(q)/dt, b₁=ω_(r)L_(q),b₂=L_(d)A, A=dI_(d)/dt.

A calculation formula of the q-axis current instruction value in thegeneral flux-weakening control stage is:I _(q)*=√{square root over (I _(max) ² −I _(d) ^(*2))}  (9)

When a Simulink control model is built, formulas (8) and (9) are writtenas an m-file to facilitate calculation of d- and q-axis currentinstruction values in the case of any electrical angular velocitysampling value in the general flux-weakening control stage.

Step (8): the MTPV control subsystem receives the electrical angularvelocity sampling value ω_(r) and the d- and q-axis current samplingvalues i_(d), i_(q), and calculates d- and q-axis current instructionvalues in the MTPV control stage.

The derivation process of the d- and q-axis current instruction valuesin the MTPV control stage considers transient current changes to improveprecise response of a torque in the MTPV control stage, enlarge thetorque output range of the motor, and achieve the purpose of enhancingspeed regulation response capabilities. After transient current changesare considered, a calculation formula of the d-axis current instructionvalue in the MTPV control stage is:

$\begin{matrix}{{\frac{{\left( {\rho - 1} \right)L_{d}A} - \sqrt{{\left( {\rho - 1} \right)^{2}L_{d}^{2}A^{2}} + {4\left( {\rho - 1} \right)\omega_{r}L_{q}C}}}{2\omega_{r}L_{q}} - \frac{C}{\sqrt{U_{\max}^{2} - \left( {{\omega_{r}L_{d}I_{d}^{*}} + {\lambda_{PM}\omega_{r}} + {L_{q}B}} \right)^{2}}}} = 0} & (10)\end{matrix}$

a calculation formula of the q-axis current instruction value in theMTPV control stage is:

$\begin{matrix}{I_{q}^{*} = \frac{C}{\left( {\rho - 1} \right)\sqrt{U_{\max}^{2} - \left( {{\omega_{r}L_{d}I_{d}^{*}} + {\lambda_{PM}\omega_{r}} + {L_{q}B}} \right)^{2}}}} & (11)\end{matrix}$

where in the formulas, ρ and C are both variables, and ρ=L_(d)/L_(q),C=ρω_(r)[λ_(PM)/L_(q)+(ρ−1)I_(d)*][L_(d)I_(d)*+λ_(PM)+BL_(q)/ω_(r)].

When a Simulink control model is built, formulas (10) and (11) arewritten as an m-file to facilitate calculation of d- and q-axis currentinstruction values in the case of any electrical angular velocitysampling value in the MTPV control stage.

In addition, the MTPV control starting point rotational speed iscalculated by combining the d and q current instruction values in theMTPV control stage and a current limit circle equation; a calculationformula is:

$\begin{matrix}\left\{ {\begin{matrix}\begin{matrix}{\frac{{\left( {\rho - 1} \right)L_{d}A} - \sqrt{{\left( {\rho - 1} \right)^{2}L_{d}^{2}A^{2}} + {4\left( {\rho - 1} \right)\omega_{Vs}L_{q}C}}}{2\omega_{Vs}L_{q}} -} \\{\frac{C}{\sqrt{U_{\max}^{2} - \left( {{\omega_{Vs}L_{d}I_{d}^{*}} + {\lambda_{PM}\omega_{Vs}} + {L_{q}B}} \right)^{2}}} = 0}\end{matrix} \\{I_{q}^{*} = \frac{C}{\left( {\rho - 1} \right)\sqrt{U_{\max}^{2} - \left( {{\omega_{Vs}L_{d}I_{d}^{*}} + {\lambda_{PM}\omega_{Vs}} + {L_{q}B}} \right)^{2}}}} \\{{I_{d}^{*2} + I_{q}^{*2}} = I_{\max}^{2}}\end{matrix}.} \right. & (12)\end{matrix}$

In the above process, a transient current change value needs to becalculated while considering transient current changes, and acalculation method is as follows:

For the general flux-weakening control stage, while not consideringtransient current changes, a voltage limit elliptic equation and acurrent limit circle equation may be combined to obtain d- and q-axiscurrent instruction values as follows:

$\begin{matrix}{\left\{ {\begin{matrix}{I_{d1} = \frac{{L_{d}\lambda_{PM}} - {L_{q}\sqrt{\lambda_{PM}^{2} + {\left( {L_{q}^{2} - L_{d}^{2}} \right)\left( {I_{\max}^{2} - \frac{U_{\max}^{2}}{\omega_{r}^{2}L_{q}^{2}}} \right)}}}}{L_{q}^{2} - L_{d}^{2}}} \\{I_{q1} = \sqrt{I_{\max}^{2} - I_{d1}^{2}}}\end{matrix}.} \right.} & (13)\end{matrix}$

Differences between I_(d1) and I_(q1) and d- and q-axis current samplingvalues I_(dr), I_(qr) are respectively calculated, and a PID regulatormay be used to calculate values of A and B in the general flux-weakeningcontrol stage, where a calculation formula is:

$\begin{matrix}{\left\{ {\begin{matrix}{A = \frac{I_{d1} - I_{dr}}{\Delta t}} \\{B = \frac{I_{q1} - I_{qr}}{\Delta t}}\end{matrix}.} \right.} & (14)\end{matrix}$

For the MTPV control stage, while not considering transient currentchanges, a voltage limit elliptic equation and an electromagnetic torqueequation may be combined to obtain d- and q-axis current instructionvalues as follows:

$\begin{matrix}\left\{ \begin{matrix}{I_{d2} = {{- \frac{\lambda_{PM}}{L_{d}}} + E}} \\{I_{q2} = \frac{\sqrt{\left( {U_{\max}/\omega_{r}} \right)^{2} - \left( {L_{d}E} \right)^{2}}}{L_{q}}} \\{E = \frac{{\rho\lambda}_{PM} - \sqrt{\left( {\rho\lambda}_{PM} \right)^{2} + {8\left( {\rho - 1} \right)^{2}\left( {U_{\max}/\omega_{r}} \right)^{2}}}}{4\left( {\rho - 1} \right)L_{d}}}\end{matrix} \right. & (15)\end{matrix}$

where E is a variable.

Differences between I_(d2) and I_(q2) and d- and q-axis current samplingvalues I_(dr), I_(qr) are respectively calculated, and the PID regulatormay be used to calculate values of A and B in the MTPV control stage,where a calculation formula is:

$\begin{matrix}\left\{ {\begin{matrix}{A = \frac{I_{d2} - I_{dr}}{\Delta t}} \\{B = \frac{I_{q2} - I_{qr}}{\Delta t}}\end{matrix}.} \right. & (16)\end{matrix}$

Step (9): the voltage decoupling control module receives the d- andq-axis current instruction values I_(d)*, I_(q)*sent from the transientcurrent planning module, and calculates d- and q-axis voltageinstructions U_(d)*, U_(q)*

Step (10): a coordinate transform module converts the d- and q-axisvoltage instructions U_(d)*, U_(q)* into U_(α) and U_(β), and a SVPWMmodule outputs a six-pulse IGBT control signal; meanwhile, an angularvelocity calculation module and a position detection module detect arotor position and an electrical angular velocity sampling value in realtime for use in the calculation of the above steps to complete motorcontrol.

As shown in FIG. 3 , the current trajectory used in the currentultra-high-speed permanent magnet synchronous motor is obtained fromsteady-state voltage and current models, and the trajectory isOA→AB₁→B₁C₁, where the section OA is a MTPA (maximum torque per ampere)control stage, the section AB₁ is a general flux-weakening controlstage, and the section B₁C₁ is a MTPV (maximum torque per volt) controlstage. Since the derivation of the trajectory does not consider theinfluence of transient current, higher torque output capability cannotbe achieved. After the influence of transient current is considered, avoltage limit ellipse will move to the upper right (the moved voltagelimit ellipse is denoted by dashed lines). At this time, the section AB₁turns into shorter AB₂, and the section B₁C₁ will also move to the upperright to become B₂C₂. At this time, the torque of the section B₂C₂ willbe larger than that of the section B₁C₁, thereby achieving a largertorque output range in the MTPV control stage.

The described embodiment is a preferred embodiment of the presentinvention, but the present invention is not limited to theaforementioned embodiment. Any obvious improvements, substitutions ormodifications that can be made by those skilled in the art withoutdeparting from the essential content of the present invention shall fallwithin the protection scope of the present invention.

What is claimed is:
 1. A transient current planning method for anultra-high-speed permanent magnet synchronous motor for improving speedregulation response capabilities, wherein the transient current planningmethod is based on a transient current planning system comprising atransient current planning module, and the transient current planningmodule comprises a MTPA control subsystem, a general flux-weakeningcontrol subsystem, a MTPV control subsystem, and a mode switchingcondition judgment subsystem; the MTPA control subsystem calculates d-and q-axis current instruction values under a MTPA control, the generalflux-weakening control subsystem calculates d- and q-axis currentinstruction values in a general flux-weakening control stage, the MTPVcontrol subsystem calculates d- and q-axis current instruction values ina MTPV control stage, the mode switching condition judgment subsystemjudges whether a control mode is the MTPA control or a generalflux-weakening control or an MTPV control, and sends the d- and q-axiscurrent instruction values in a corresponding control mode to a voltagedecoupling control module, and the voltage decoupling control modulecalculates d- and q-axis voltage instruction values for controlling theultra-high-speed permanent magnet synchronous motor; the transientcurrent planning method comprises the following steps: step (1):judging, by the mode switching condition judgment subsystem, whether toswitch to the general flux-weakening control or the MTPV control, and ifyes, entering step (2); otherwise, entering step (5), wherein switchingor not is determined by judging whether d- and q-axis voltage valuesreach limit values as a switching point, and a judgment formula is:√{square root over (U _(d) ² +U _(q) ²)}<U _(max) if the judgmentformula is established, switching to the MTPA control is performed;otherwise, the transient current planning method turns to step (2); step(2): judging, by the mode switching condition judgment subsystem,whether a rotational speed sampling value ω_(r) is greater than a MTPVcontrol starting point rotational speed ω_(Vs), and if not, enteringstep (3); if yes, entering step (4); step (3): receiving, by the generalflux-weakening control subsystem, d- and q-axis current instructionvalues I_(d)* and I_(q)* in a MTPA control stage and the rotationalspeed sampling value, and calculating the d- and q-axis currentinstruction values in the general flux-weakening control stage, whereina d-axis current instruction value in the general flux-weakening controlstage is:a ₁ ² I _(d)*²+2a ₁ a ₂ I _(d) *+a ₂ ² +b ₁ ²(I _(max) ² −I _(d)*²)+b ₂²+2b ₁ b ₂√{square root over (I _(max) ² −I _(d)*²)}=U _(max) ² wherein,a₁, a₂, b₁, b₂, A, and B are all variables, and a₁=ω_(r)L_(d),a₂=ω_(r)λ_(PM)+L_(q)B, B=dI_(q)/dt, b₁=ω_(r)L_(q), b₂=L_(d)A,A=dI_(d)/dt; I_(max) is a maximum stator current, λ_(PM) is a permanentmagnet flux linkage, L_(d) is a d-axis inductance, L_(q) is a q-axisinductance, I_(q) is a q-axis current instruction initial value, andI_(d) is a d-axis current instruction initial value; a q-axis currentinstruction value in the general flux-weakening control stage is:I _(q)*=√{square root over (I _(max) ² −I _(d)*²)} step (4): receiving,by the MTPV control subsystem, the rotational speed sampling value ω_(r)and d- and q-axis current sampling values i_(d) and i_(q), andcalculating the d- and q-axis current instruction values in the MTPVcontrol stage, wherein a calculation formula of a d-axis currentinstruction value in the MTPV control stage is:${\frac{{\left( {\rho - 1} \right)L_{d}A} - \sqrt{{\left( {\rho - 1} \right)^{2}L_{d}^{2}A^{2}} + {4\left( {\rho - 1} \right)\omega_{r}L_{q}C}}}{2\omega_{r}L_{q}} - \frac{C}{\sqrt{U_{\max}^{2} - \left( {{\omega_{r}L_{d}I_{d}^{*}} + {\lambda_{PM}\omega_{r}} + {L_{q}B}} \right)^{2}}}} = 0$a calculation formula of a q-axis current instruction value in the MTPVcontrol stage is:$I_{q}^{*} = \frac{C}{\left( {\rho - 1} \right)\sqrt{U_{\max}^{2} - \left( {{\omega_{r}L_{d}I_{d}^{2}} + {\lambda_{PM}\omega_{r}} + {L_{q}B}} \right)^{2}}}$wherein, ρ and C are both variables, and ρ=L_(d)/L_(q),C=ρω _(r)[λ_(PM) /L _(q)+(ρ−I)I _(d) *][L _(d) I _(d)*+λ_(PM) +BL_(q)/ω_(r)]; and step (5): receiving, by the voltage decoupling controlmodule, the d- and q-axis current instruction values sent by thetransient current planning module and calculating d- and q-axis voltageinstructions, so as to implement a control over the ultra-high-speedpermanent magnet synchronous motor.
 2. The transient current planningmethod of the transient current planning system for the ultra-high-speedpermanent magnet synchronous motor according to claim 1, wherein aprocess of obtaining the d- and q-axis current instruction values in theMTPA control stage is: judging whether I_(q) is greater than a maximumq-axis current I_(qmax1), wherein if yes, a first calculation formula ofthe d- and q-axis current instruction values is:$\left\{ {\begin{matrix}{I_{d}^{*} = {\frac{\lambda_{PM}}{4\left( {L_{q} - L_{d}} \right)} - \sqrt{\frac{\lambda_{PM}^{2}}{16\left( {L_{q} - L_{d}} \right)^{2}} + \frac{I_{\max}^{2}}{2}}}} \\{I_{q}^{*} = {{{sign}\left( n^{*} \right)}\sqrt{I_{\max}^{2} - I_{{dmax}1}^{2}}}}\end{matrix};} \right.$  if not, a second calculation formula of the d-and q-axis current instruction values is: $\left\{ {\begin{matrix}{I_{d}^{*} = {\frac{\lambda_{PM}}{4\left( {L_{q} - L_{d}} \right)} - \sqrt{\frac{\lambda_{PM}^{2}}{16\left( {L_{q} - L_{d}} \right)^{2}} + I_{q}^{2}}}} \\{I_{q}^{*} = I_{q}}\end{matrix},} \right.$  wherein sign(n*) is a sign function.
 3. Thetransient current planning method of the transient current planningsystem for the ultra-high-speed permanent magnet synchronous motoraccording to claim 2, wherein a calculation formula of the maximumq-axis current I_(qmax1) is: $\left\{ {\begin{matrix}{I_{{dmax}1} = {\frac{\lambda_{PM}}{4\left( {L_{q} - L_{d}} \right)} - \sqrt{\frac{\lambda_{PM}^{2}}{16\left( {L_{q} - L_{d}} \right)^{2}} + \frac{I_{\max}^{2}}{2}}}} \\{I_{{qmax}1} = \sqrt{I_{\max}^{2} - I_{{dmax}1}^{2}}}\end{matrix},} \right.$  wherein I_(dmax1) is a maximum d-axis currentunder the MTPA control.
 4. The transient current planning method of thetransient current planning system for the ultra-high-speed permanentmagnet synchronous motor according to claim 1, wherein the q-axiscurrent instruction initial value is obtained from$T_{e} = {{\frac{\omega_{ref} - \omega_{r}}{\Delta t}J{and}T_{e}} = {\frac{1}{2}{n_{p}\left\lbrack {{\lambda_{PM} + \sqrt{\left. {\lambda_{PM}^{2} + {4{I_{q}^{2}\left( {L_{d} - L_{q}} \right)}^{2}}} \right\rbrack I_{q}}},} \right.}}}$ wherein T_(e) is an electromagnetic torque, ω_(ref) is a targetrotational speed, Δt is a sampling interval, J is a shaft moment ofinertia, and n_(p) is a number of pole-pairs.
 5. The transient currentplanning method of the transient current planning system for theultra-high-speed permanent magnet synchronous motor according to claim1, wherein the MTPV control starting point rotational speed iscalculated by combining the d- and q-axis current instruction values inthe MTPV control stage and a current limit circle equation, specificallyas follows: $\left\{ {\begin{matrix}{\frac{{\left( {\rho - 1} \right)L_{d}A} - \sqrt{{\left( {\rho - 1} \right)^{2}L_{d}^{2}A^{2}} + {4\left( {\rho - 1} \right)\omega_{Vs}L_{q}C}}}{\omega_{Vs}L_{q}} -} \\{\frac{C}{\sqrt{U_{\max}^{2} - \left( {{\omega_{Vs}L_{d}I_{d}^{*}} + {\lambda_{PM}\omega_{Vs}} + {L_{q}B}} \right)^{2}}} = 0} \\{I_{q}^{*} = \frac{C}{\left( {\rho - 1} \right)\sqrt{U_{\max}^{2} - \left( {{\omega_{Vs}L_{d}I_{d}^{*}} + {\lambda_{PM}\omega_{Vs}} + {L_{q}B}} \right)^{2}}}} \\{{I_{d}^{*2} + I_{q}^{*2}} = I_{\max}^{2}}\end{matrix}.} \right.$
 6. The transient current planning method of thetransient current planning system for the ultra-high-speed permanentmagnet synchronous motor according to claim 1, wherein values of A and Bin the general flux-weakening control stage are: $\left\{ \begin{matrix}{A = \frac{I_{d1} - I_{dr}}{\Delta t}} \\{B = \frac{I_{q1} - I_{qr}}{\Delta t}}\end{matrix} \right.$ wherein I_(dr) and I_(qr) are respectively d- andq-axis current sampling values; I_(d1) and I_(q1) are respectively thed- and q-axis current instruction values in the general flux-weakeningcontrol stage, specifically as follows: $\left\{ {\begin{matrix}{I_{d1} = \frac{{L_{d}\lambda_{PM}} - {L_{q}\sqrt{\lambda_{PM}^{2} + {\left( {L_{q}^{2} - L_{d}^{2}} \right)\left( {I_{\max}^{2} - \frac{U_{\max}^{2}}{\omega_{r}^{2}L_{q}^{2}}} \right)}}}}{L_{q}^{2} - L_{d}^{2}}} \\{I_{q1} = \sqrt{I_{\max}^{2} - I_{d1}^{2}}}\end{matrix}.} \right.$
 7. The transient current planning method of thetransient current planning system for the ultra-high-speed permanentmagnet synchronous motor according to claim 1, wherein values of A and Bin the MTPV control stage are: $\left\{ \begin{matrix}{A = \frac{I_{d2} - I_{dr}}{\Delta t}} \\{B = \frac{I_{q2} - I_{qr}}{\Delta t}}\end{matrix} \right.$ wherein I_(d2) and I_(q2) are respectively the d-and q-axis current instruction values in the MTPV control stage,specifically as follows: $\left\{ \begin{matrix}{I_{d2} = {{- \frac{\lambda_{PM}}{L_{d}}} + E}} \\{I_{q2} = \frac{\sqrt{\left( {U_{\max}/\omega_{r}} \right)^{2} - \left( {L_{d}E} \right)^{2}}}{L_{q}}} \\{E = \frac{{\rho\lambda}_{PM} - \sqrt{\left( {\rho\lambda}_{PM} \right)^{2} + {8\left( {\rho - 1} \right)^{2}\left( {U_{\max}/\omega_{r}} \right)^{2}}}}{4\left( {\rho - 1} \right)L_{d}}}\end{matrix} \right.$ wherein, E is a variable.